SOA-C02 Cost and Performance Optimization Practice Question
A SysOps administrator notices that an EC2 instance's CPU utilization is consistently above 90% during peak hours. Which action will improve performance without over-provisioning resources?
⚠ Common exam trap
Many exam-takers confuse horizontal scaling (Auto Scaling) with vertical scaling, assuming adding more instances is always the best performance fix, but the question explicitly asks to avoid over-provisioning, making a single larger instance the more efficient choice.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Change the instance type to a larger size, such as moving from t3.medium to t3.large.
Changing the instance type to a larger size (e.g., from t3.medium to t3.large) vertically scales the instance, providing more vCPUs and memory to handle the increased CPU load during peak hours. This directly addresses the high CPU utilization without over-provisioning, as you are only scaling up the specific resource that is constrained. Spot Instances (A) do not improve performance; they offer lower cost but same performance. Increasing EBS volumes (B) does not affect CPU performance. Auto Scaling (D) adds more instances (horizontal scaling), which can over-provision if the single instance's capacity is sufficient after a vertical scale-up.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use Spot Instances instead of On-Demand.
Why it's wrong here
Spot Instances are the same physical and virtual hardware as On-Demand instances, offering identical vCPU and memory specifications; the lower price is achieved through excess capacity bidding, not by providing more compute power. Switching to Spot would not increase the instance's processing capability, so CPU utilization would remain precisely as high as before. Furthermore, Spot Instances are subject to two-minute interruption notices, which can destabilize workloads that need consistent CPU performance, making them unsuitable for a sustained CPU bottleneck.
- ✗
Increase the number of EBS volumes attached to the instance.
Why it's wrong here
Amazon EBS volumes are durable block-level storage devices that connect to an EC2 instance via the network, and their per-instance aggregate performance is governed by IOPS/throughput limits independent of the CPU. Increasing the number of EBS volumes or using Provisioned IOPS only expands storage bandwidth and I/O concurrency; it does not add arithmetic or processing capacity to the instance's vCPUs. A CPU utilization problem is caused by compute saturation, not by storage starvation, so this change would leave the observed metric untouched.
- ✓
Change the instance type to a larger size, such as moving from t3.medium to t3.large.
Why this is correct
Resizing the EC2 instance to a larger type, such as changing from t3.medium to t3.large, is a vertical scaling operation that allocates more compute resources to the same virtual machine. A larger instance type typically provides more vCPUs, higher baseline CPU performance, and more memory, directly increasing the capacity to process instructions without queueing, thereby reducing CPU utilization. For t3 families, the larger size also raises the CPU credit earning rate and baseline (e.g., from 20% to 30% for medium to large), so even modest workloads experience fewer credit exhaustions and less throttling.
- ✗
Configure Auto Scaling to add more instances during peak hours.
Why it's wrong here
Configuring Auto Scaling to add additional EC2 instances during peak hours is a horizontal scaling strategy that spreads incoming traffic across multiple machines, potentially reducing the load on any single instance. However, it does not increase the compute capacity of the existing instance that is already showing high CPU utilization, so that particular instance may remain saturated if it is processing a stateful or monolithic application without a load balancer. Horizontal scaling also introduces architectural requirements such as application-level load balancing, statelessness, and possibly database connection management, which are more complex than simply enlarging the instance.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SOA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SOA-C02 exam.